PROJECT SUMMARY/ABSTRACT Young men who have sex with men (YMSM; ages 18-29 years) have rising HIV incidence in the United States. Pre-exposure prophylaxis (PrEP) is a highly effective medication prevent HIV infection, both at the individual and population level. However, in several clinical trials and demonstration projects among YMSM, a majority of participants had adherence to PrEP sufficiently low to compromise efficacy throughout the study. Unfortunately, pill-counts and self-reported adherence have limitations in this population, and therapeutic drug monitoring using previously available methods requires expensive equipment and specialized staff, meaning it cannot be implemented at the point-of-care (POC). We have developed a novel POC test to measure urine drug-levels to PrEP for the first time, providing the opportunity to target and enhance adherence counseling during a routine clinical visit. Substantial knowledge gaps on the correct counseling approach and framing of the drug-level feedback message must be addressed to use this strategy to improve adherence among YMSM. The proposed training and research plan for this K23 application will allow Matthew Spinelli, MD to acquire the necessary skills to achieve his career goal of becoming an NIH-funded independent clinical investigator with expertise in designing interventions to improve antiretroviral adherence among men who have sex with men (MSM). Under the guidance of a dedicated mentoring team, Dr. Spinelli will use a mixed methods approach to test the central hypothesis that an intervention leveraging a POC urine bioassay to detect PrEP adherence can both target and enhance adherence counseling. Brief interventions are a motivational interviewing (MI) counseling approach with wide uptake by primary care providers for substance use prevention and medical therapy adherence. Dr. Spinelli proposes a brief intervention be used as the framework for POC drug-level feedback among YMSM using PrEP at the San Francisco City Clinic (SFCC). SFCC is the municipal sexually- transmitted disease clinic for San Francisco and has a high-volume PrEP program, facilitating recruitment. Building on the candidate's prior research in PrEP care outcomes and adherence diagnostics, this proposal will address the following specific aims: (1) identify behavioral targets for PrEP adherence amenable to counseling specific to YMSM; (2) develop the POC bioassay-enhanced adherence brief intervention through in-depth interview feedback from PrEP users and providers; (3) test the acceptability, feasibility, and preliminary impact on long-term adherence, measured through hair tenofovir levels, of the brief intervention in a pilot randomized controlled trial among YMSM. This proposed research plan has the goal of optimizing PrEP's impact through a novel adherence support and is aligned with Dr. Spinelli's career development plan to gain expertise in intervention design, qualitative research, and behavioral trial design and evaluation. The findings of this proposal will lead to a R01 application to test a POC bioassay-enhanced adherence brief intervention among YMSM in a multi-city trial, with the goal of reducing the burden of HIV among MSM.